The present invention relates to defibrillation techniques, and in particular relates to atrial defibrillation.
Atrial fibrillation (often referred to simply as AF), in its chronic and paroxysmal forms, constitutes the arrhythmia that is most frequent in the population, with a particularly high incidence (10%) in adults aged over 65 years. There is no pharmacological treatment which is sure to be effective and, as for all antiarrhythmic drugs, there is an increased probability of inducing serious ventricular proarrhythmia. In patients who are suffering from this condition to an incapacitating extent and who do not respond to the use of an average of two to three antiarrhythmia drugs, the subject of an alternative solution becomes important.
An implantable atrial defibrillator with an associated ventricular stimulation/sensing capability constitutes a recent treatment which is currently at the clinical evaluation stage. A defibrillator of this type is usually implanted by the insertion in the heart of two electrodes (leads) having large active surface areas and constituted by metal coils which are positioned along the outer wall of the right atrium and in the coronary sinus, whilst the metal container of the defibrillator can also operate as an active pole during discharge.
The basic object of defibrillation is to produce an electric field adequate to involve, anatomically, a significant portion of the myocardium of both atria, in order to depolarize, by means of the electric shock, a predominant number of myocardial cells which are subject to spontaneous, chaotic and non-synchronized electrical activity. Recent tests have shown the great importance of the distribution of the electric field in minimizing defibrillation energy and consequently voltage, muscle-stimulation and perception of pain, which constitutes the most important factor limiting the use of these devices.
The object of the present invention is to provide a defibrillator which can achieve an effective action antagonistic to fibrillation.
In one aspect, this invention is an implantable defibrillator apparatus comprising a plurality of defibrillation electrodes adapted to be applied to the heart muscle and to deliver electric defibrillation shocks thereto, the plurality of electrodes in communication with defibrillation-control means capable of selectively supplying voltage pulses to the electrodes, wherein the defibrillation control means controls the duration and interval of the voltage pulses and further wherein the voltage pulses produce electric defibrillation shocks sufficient to produce defibrillation. Preferably, the electric defibrillation shocks are sufficient to produce defibrillation synchronized with the heart""s QRS, and the control unit can deliver defibrillation shocks to the electrodes in a desired time sequence. The control unit may selectively vary at least one characteristic of the electric defibrillation shocks, including the waveform of the defibrillation shock, the duration of the defibrillation shock, the interval between successive defibrillation shocks, and the electrodes to which a defibrillation shock is applied at any particular time. The apparatus may also comprise sensor means for detecting the occurrence of a fibrillation phenomenon, the sensor means being connected to the control unit and adapted to activate the application of defibrillation shocks. The sensor means may comprise respective sensing lines that connect the plurality of electrodes to the control unit to enable the electrodes to act both as defibrillation electrodes and as sensing electrodes. The apparatus may also comprise sensor means capable of detecting a ventricular electrogram. The control unit may synchronize the application of defibrillation shock during the QRS of the electrogram.
In another aspect, this invention is an implantable defibrillator apparatus comprising a plurality of defibrillation electrodes adapted to be applied to the heart muscle and to deliver electric defibrillation shocks thereto; the plurality of electrodes in communication with electronic switches; the electronic switches in communication with a power stage capable of supplying voltage pulses to the electrodes, wherein the power stage is connected to a control unit that controls the duration and interval of the voltage pulses and further wherein the voltage pulses are applied for a time sufficient to produce defibrillation.
In yet another aspect, this invention is a method of treating atrial fibrillation comprising providing a stimulating device having a plurality of electrodes; inserting the plurality of electrodes at desired locations in the heart; and applying defibrillation shocks to the plurality of electrodes in a desired sequence, thereby creating an electric field having a geometry designed for the patient""s anatomy. Sensing atrial fibrillation may be done by means of the plurality of electrodes or by means of a specialized sensor.